[trishieldchief]

Cliff
Just to clarify, you have experience that a Summit 2802 cam is an excellent choice for a stock 10.5 static compression 69 RA III 400, M20 4 speed, 3.55 posi 69 GTO that will operate on 94 octane pump gas?

Originally Posted by Cliff R

"The 744 cam (Melling SPC-3) has TERRIBLE valve train dynamics. This is indeed due to the "square lobes" which are in reality just the nose of the cam lobe being concentric with the centerline of the camshaft in order to increase duration without increasing lift. You are much better off with a cam with a "modern" profile such as a Summit 2802 (224 deg duration at 0.050 on intake) that has good valve train dynamics."

+2 and very well said.

The 2802 is a very good choice for a 400 engine with relatively high compression on pump fuel. We have quite a few customers using that cam with great success, including nice street manners and running well at the track.

I use and prefer the Crower 60243 camshaft for manual trans applications with at least 3.55 gears and 400 engines. It works equally as well in 428's with a little less compression, and the 455's down around 9 to 1 compression.

As far as the Summit rating of the 2802 camshaft, they don't even mention what size engine, or the true static compression ratio of the engine. It would be a complete "turd" in a Pontiac 350 engine with anything less than 9 to 1 compression, and nearly perfect for a 400 engine at 10 to 1 compression, for example.

The static compression ratio plays a HUGE role in camshaft selection with any particular engine. For example, the 2800 is a great cam for a 400 engine down at 8 to 1. Idles great, strong off idle, smooth and lower rpm's, and pulls very hard in the mid-range.

For a 9 to 1 compression 400 move up to the 2801 and you will find the same nice qualities from your engine with stronger power in the upper mid-range and top end.

At 10 to 1 compression the 2802 becomes the better cam choice, as it idles nice, strong off idle and pulls even harder in the upper mid-range and top end.

Take the 2802 and put it in a 400 engine at 8 to 1 compression, it's "lazy", idles with low vacuum, "soggy" off idle and not really any useable power below about 2800rpm's. It will still pull really well in the higher rpms, as the static compression ratio becomes less of a player in power production as the events are happening much faster, and power production becomes more about moving air and VE than exactly how hard the engine is squeezing the incoming mixture.

We sort of found this out quite a few years ago with a 455 engine. A new employee at KRE was given the task of hand porting a set of 6X heads for a 455 engine. He spent many hours on them, and did a fantastic job. No one noticed that he had selected a set of 6H heads by mistake, and that the 455 engine was only going to end up being very low compression. They went ahead with the engine build anyhow, using the Crower RAIV clone 60919 camshaft. That cam fairs very well in a 455 up near 10 to 1 compression, but even there is idles pretty low vacuum and real power curve starts around 2800rpm's or so. It will easily make 1hp/cid with 230cfm or more airflow.

Dyno time came and the low compression 455 made nearly the same numbers as a higher compression 455 with the same basic parts. It did however idle very poorly due to the low static compression ratio. Keep in mind when reading this that the dyno pulls started past 3000rpm's, and a dyno has no way to tell us how well an engine will run in a vehicle for "normal" driving.

One also has to remember when it comes to this topic, is that we are trying to build an engine that uses pump gas. The camshaft becomes equally if not more important here than the static compression ratio. We need to choose a cam that will make good cylinder pressure at idle and lower rpm's for decent idle quality and smooth power in the "normal" driving range, but not so small that it pulls all the power down in the rpm range and detonates on pump fuel.

This is why a small cam like the 2800 is a perfect choice for a 400 engine at 8 to 1 compression, but will pound like sledgehammers in the same engine at 10 to 1 compression. It simply does too good a job of cylinder filling and peak torque too early in the rpm range. The engine will act about 1-2 points higher in compression than what it is, and rattle just about everyplace on low octane fuel.

Anyhow, as it relates to this topic, the 2802 cam would be a great choice for the 421 build with 9.6 to 1 compression, manual trans, and 3.36 gearing. In comparison, I built and installed a 428 engine into my Ventura in the early 1990's. It was topped with #96 heads and used the 744 camshaft. It was about the biggest "turd" of an engine that ever sat between the fenders. Idled poorly, "soggy" at low rpm's, and absolutely DONE pulling by 4500rpm's. To this day I don't know if I just didn't have it degree'd correctly, and/or not enough valve spring on it, etc. That engine didn't last long so I built another one, using 6X-4 heads and HC-01a camshaft. The new engine idled better, strong off idle, and would tear your head slam off the entire loaded rpm range. That engine stayed in place for over 10 years until I moved up to my first 455 engine.....Cliff